We have continued our investigations of the molecular mechanism of recombination in Bacillus subtilis. Our system involves the use of genetic transformation, and we are currently studying the role of several enzymes in this process. Our evidence suggests that DNA polymerases I and III play a role in the integration of transforming DNA, although the presence of either one of these enzymes is sufficient. We have also isolated several nuclease-deficient mutants which simultaneously become transformation-deficient. The nature of the lesion in these strains is under study. We have also obtained evidence suggesting that donor DNA is preferentially inserted in the most recently synthesized strand of the recipient double helix. BIBLIOGRAPHIC REFERENCES: Dubnau, D.: Genetic transformation of Bacillus subtilis: A Review with Emphasis on the Recombination Mechanism. In: Microbiology-1975 (American Society for Microbiol.)